Interface-Mediated Phase Selection in Multi-Component Silicide Thin Films

Multi-component silicide thin films represent an emerging class of high-entropy ceramics, yet their phase formation mechanisms remain poorly understood. In this work, (CrMnFeCoNi)Si thin films have been deposited using two different approaches. In the first, Cantor alloy and silicon were co-sputtered on a silicon substrate at room temperature, producing X-ray amorphous films. In the second, a two-step process was employed: deposition of a CrMnFeCoNi (450 nm) / Si (750 nm) bilayer on a Si substrate with a TiN diffusion barrier, followed by post-annealing. While CALPHAD thermodynamic calculations predict single B20-phase stability at equiatomic metal-to-silicon stoichiometry in the 650-850°C range, and bulk synthesis of single-phase (CrMnFeCoNi)Si has been demonstrated, our annealed films exhibit phase segregation into three distinct silicide structures: B20-type (CrMnFeCoNi)Si (~42.0(6) wt%), fluorite-type (CoNiFe)Si 2 (~37.5(6) wt%), and C40-type (CrMn)Si 2 (~16.8(4) wt%). Through combined X-ray diffraction, transmission electron microscopy, in-situ heating experiments, and CALPHAD modeling, we demonstrate that interdiffusion between the bilayer components leads to local silicon enrichment (Si/metal > 1.2), thereby shifting the system outside the single-phase compositional window. Under these silicon-rich conditions, the preferential silicide-forming tendencies of individual elements dominate, with disilicide phases nucleating first at 450-500°C due to lower activation barriers. The limited diffusion lengths inherent to thin film geometries (~10-100 nm) prevent subsequent homogenization into a single phase. These results establish that achieving the precise stoichiometric conditions required for single-phase formation in this system is inherently challenging in thin film architectures where interdiffusion governs the local composition, and identify interface engineering and rapid thermal processing as critical strategies for controlled synthesis.